This invention concerns an improvement in the design of air-cooled steam condensing bundles used in vacuum steam condensers serving steam turbine power cycles and the like where contaminated steam is condensed inside these bundles that are of single-row two-pass construction. Two-pass steam condensers have some desirable freeze abatement features but they also inherently introduce some unbalanced flow-distribution problems amongst the typical 1st-pass tubes and bundles because of lengthy steam flow distances and fan air-flow velocity profile distortions across the face of the bundles. The 1st pass tubes and bundles located furthest from the 2nd-pass tubes and bundles do not flow their design intended share of steam/gas mixture so that they become vulnerable to freezing. In addition, the dephlegmators are built as separate bundles or fan cells that are operated with cold ambient air. This invention addresses this problem by dividing the conventional size bundle into small mini-bundle groups of identically constructed sets. These sets feature one centrally located 2nd-pass tube with symmetrically placed 1st-pass tubes positioned on either side and with a new steam equalizing baffle installed at the ends of the 1st-pass tubes. The bundle thermal performance characteristics are established in part by the number of 2nd-pass tube sets that are incorporated into the bundle. The more mini-bundles and 2nd-pass tubes installed in a bundle, the greater the 1st-pass freeze protection in a suddenly dropping steam-load situation.
The background art of air-cooled steam condensers features many different bundle designs. They generally vary from 1 to 4 tube rows and are of 1, 2 or 3 pass design. Some steam condensers presently on the market do have 1st-pass main steam condensing tubes and 2nd-pass after-condenser tubes. They are sometimes called Condenser/Dephlegmator bundles that are installed in separate fan cells. They also are labeled as First Stage/Second Stage bundles that are installed in the same fan cell. Another type has its Primary Zone/Secondary Zone steam condenser sections built into the same bundle.
None of the prior art one-row two-pass bundles address the problem of uneven steam mixture flows from 1st-pass tubes nor do they feature the grouping of 1st-pass tubes around singular 2nd-pass tubes nor do they have a flow equalizing device installed at the end of the 1st-pass tubes as revealed in this invention. Their 1st-pass tubes flow unequal quantities of steam into the 2nd-pass tubes due to differences in fan air-flow profile distortions and differences in their physical locations with the result that those 1st-pass tubes providing the least mixture are the ones that are the most subject to freezing.
The more common and obvious patents in this field are listed below along with a brief comment on their basic fluid flow design features.
1. Howard, U.S. Pat. No. 2,217,410 has a four-row two-pass design with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid control leaving the 1st-pass tubes.
2. Howard, U.S. Pat. No. 2,247,056 has a four-row two-pass design with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid control leaving the 1st-pass tubes.
3. McElgn, U.S. Pat. No. 2,816,738 has a four-row two-pass construction with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid flow control leaving the 1st-pass tubes.
4. Neimann, U.S. Pat. No. 3,289,742 has a four-row single-pass condenser with a separate 2nd-pass bundle called a dephlegmator with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid flow control leaving the 1st-pass tubes.
5. Gunter, U.S. Pat. No. 3,543,843 has a four-row single-pass design and a four-row two-pass design where the 2nd-pass is a separate bundle. There is no grouping of 1pass tubes around singular 2nd-pass tubes in the same bundle nor fluid flow control leaving the 1st-pass tubes.
6. Dehne, U.S. Pat. No. 3,556,204 has a four-row two-pass condenser with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid flow control leaving the 1st-pass tubes.
7. Staub, U.S. Pat. No. 3,677,338 has a four-row single-pass condenser.
8. Schoonman, U.S. Pat. No. 3,705,621 has a four-row two-pass design with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid control leaving the 1st-pass tubes.
9. Modine, U.S. Pat. No. 3,707,185 has a three-row single-pass condenser.
10. Schoonman, U.S. Pat. No. 3,887,002 has a four-row two-pass design for the main section and a similar construction but smaller after-condenser section. There is no grouping of 1st-pass tubes around singular 2nd-pass tubes in the bundle nor fluid flow control leaving the 1st-pass tubes.
11. Russ, U.S. Pat. No. 3,976,126 has a single-row single-pass tube condenser flowing into a separate single-row single-pass dephlegmator with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid flow control leaving the 1st-pass tubes.
12. Larinoff, U.S. Pat. No. 4,129,180 has a four-row single-pass design constituting the "main portion" and a built-in "vent condenser portion" with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle for fluid flow control leaving the 1st-pass tubes.
13. Kluppel, U.S. Pat. No. 4,168,742 has a single-row single-pass design with some of the tubes divided into two channels in which the second channel is the 2nd-pass used for the removal of noncondensible gases from the outlet header. There is no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid flow control leaving the 1st-pass tubes.
14. Gatti, U.S. Pat. No. 3,177,859 has a four-row two-pass design with the first three rows constituting the first condensation zone and the fourth and last row being the second condensation zone. There is no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid flow control leaving the 1st-pass tubes.
15. Gerz, U.S. Pat. No. 4,190,102 has a three-row single-pass condenser and a separate three-row single-pass Dephlegmator design with no grouping of 1st-pass tubes around singular 2-nd-pass tubes in the same bundle nor fluid control leaving the 1st-pass tubes.
16. Berg, U.S. Pat. No. 4,202,405 has a four-row two-pass design with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid flow control leaving the 1st-pass tubes.
17. Zanobini, U.K. Patent No. 2,093,176 has a three-pass bundle with three-rows with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid flow control leaving the 1st-pass tubes.
18. Minami, U.S. Pat. No. 4,417,619 has a four-row bundle of two-pass design with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid flow control leaving the 1st-pass tubes.
19. Henry, U.K. Patent No. 2,137,330 has fluid flow restrictors at the end of the 1st-pass but has no 2nd-pass in his bundle.
20. Larinoff, U.S. Pat. No. 4,903,491 has a four-row single-pass condenser design.
21. Larinoff, U.S. Pat. No. 4,905,474 has a four-row single-pass condenser design.
22. Larinoff, U.S. Pat. No. 4,926,931 has a four-row two-pass condenser design with no grouping of 1st-pass tubes around singular 2nd-pass tubes in the same bundle nor fluid flow control leaving the 1st-pass tubes.
At first glance the Kluppel single-row design condenser U.S. Pat. No. 4,168,742 appears to have some similarities to this invention but on detailed examination they have little in common. Kluppel's object is the design of a single-row steam condensing bundle employing new extended surface tubes and the removal of noncondensible gasses from the outlet header by means of a venting channel that also functions as a vent condenser. Larinoff's object is to minimize the adverse effects of fan airflow velocity profile distortions across the face of the bundles and to equalize steam flows from all the st-pass tubes of a single-row steam condensing bundle by decreasing the flow travel distances between the 1and 2nd-passes and throttling the steam mixture discharges from the 1st-pass by means of a new baffle plate Kluppel's design is a "single pass arrangement" (Col. 1, line 14) with a "relatively small number of divided tubes" (Col 5, line 4) venting the outlet header. Larinoff's design is a two-pass arrangement with possibly as many as half of the bundle tubes operating in the 2nd-pass in a Condenser/Dephlegmator mode. Kluppel employs two different types and sizes of tubes for the 1and 2nd-pass (Col 4, line 15) as shown in FIGS. 6 and 7. Larinoff has only one size of tube that is used in both the 1st-pass and 2nd-pass. Kluppel does not group the 1st-pass tubes (18 and 24) symmetrically on either side of the 2nd-pass channel (23) as evidenced in FIG. 5 where the two 2nd-pass tubes (19/23) are positioned against the ends of the header (14). Larinoff groups all of his 1st-pass tubes on either side of his 2nd-pass tubes. Kluppel's 2nd-pass tube (23) is not geometrically centered (FIG. 5) amongst the 1st-pass tubes to attempt to balance the fluid forces that flow the steam/gases from the 1st-pass tubes (18) into the 2nd-pass tubes (23). Larinoff geometrically centers his 2nd-pass tubes and in addition equalizes the fluid forces from each tube by the use of flow equalizing baffle. Kluppel's 2nd-pass tube (23) section is purposely located in the upper heated portion of the tube (19) above the 1st-pass to heat its vapor contents (Col 4, line 53) whereas Larinoff's 2nd-pass tubes are the same as the 1st-pass tubes which are exposed to the ambient air. In reality, Kluppel's steam condensing tubes (18) that are adjacent to the 2nd-pass channel(23) are the ones that supply most of the steam mixture entering the 2nd-pass channel (23). The rest of the tubes suffer with stagnant gas pockets. In addition to its poor steam mixture flow to the 2nd-pass channel, the design is fundamentally flawed in its fluid flow. Kluppel connects a large cross-section tube FIG. 7 to a smaller cross-section tube shown in the lower portion of FIG. 6. Each of these tubes condenses different qualities of steam hence have different steam pressure drops. The net result is that in operation the steam either flows out of the lower portion of the tube (19) into the upper portion (23), which upsets the bundle gas removal process, or forms a stagnant pocket of noncondensible gases at the lower end of the FIG. 6 tubes. In either case it is a flawed design; fluid dynamics teaches never to connect two different diameter steam condensing tubes to the same inlet and outlet headers because they have different steam pressure drops. This causes steam to flow between tube ends in the outlet header and that is one of the major reasons for gas pockets and tube freezing.
In the review of the prior art of two-pass steam condensers there is an important design and operating feature that requires explanation. This is the feature that concerns the size of the steam condensing capability of the 2nd-pass. Some designs merely employe one or several 2nd-pass tubes in their bundle such as Larinoff U.S. Pat. No. 4,129,180 and Kluppel U.S. Pat. No. 4,168,742 that amount to about 2% to 4% of the total steam condensing capacity of the bundle. Other designs use an entire row of 2nd-pass tubes such as Gatti U.S. Pat. No. 4,177,859 which amount to 25% of the tubes but only about 10% of the total steam condensing capacity. Ruff U.S. Pat. No. 3,976,126 uses separate fan cells for the 2nd-pass bundles and they have been known to use as much as 33% of their total tubes and steam condensing capacity in 2nd-pass service.
This wide difference in the steam condensing capacity of the 2nd-pass section ranging from 2% to 33% reflects the differences in industry practice. Some manufacturers assign a purely gas vent-condenser role to the 2nd-pass tubes and they represent the 2% figure. Others assign a much broader role to the 2nd-pass tubes that involves not only the gas gathering chore but also a freeze protection contribution and they represent the 33% figure. The 2% 2nd-pass designs are generally referred to as vent-tubes while the 33% 2nd-pass designs are called Dephlegmators and secondary condensers.
The gas gathering and concentrating chore of the 2nd-pass vent tube and Dephlegmator is readily understood. The freeze protection contribution of the 2nd-pass tubes in Dephlegmators and secondary condensers requires some explanation. The Dephlegmators in A-frame condensers have their 2nd-pass tubes oriented such that the steam flows up into the tube while the condensate flows down counterflow through the steam. The thought behind this being that as long as there is steam in the 2nd-pass tubes, the condensate flowing downward through the steam cannot freeze. This design feature comes into play when there is a sudden drop in turbine exhaust steam load in freezing weather with the fans still delivering their original air quantity. This could present a dangerous freeze situation to the 2% 2nd-pass designs but not necessarily to the 33% 2nd-pass designs. The steam supply can drop 33% in this condenser which will rob all the steam in the 2nd-pass but will not jeopardize the integrity of the more vulnerable 1st-pass tubes. Incorporating such a large quantity of 2nd-pass tubes into the condenser is a form of operating insurance against certain types of potentially freezing situations. By contrast, the lower cost bundle built with vent tubes that have only 2 to 4% 2nd-pass tubes can only sustain a 2 to 4% drop in steam load before the 1st-pass tubes are exposed. This small steam capacity of the 2nd-pass section has a negligible influence on freeze protection with dropping steam loads.
Since industry practice is to condense from 2% to 33% or more of the 2nd-pass steam, the bundle of this invention must accommodate this wide range of needs. It is designed to accommodate from one 2nd-pass tube per bundle to fifty percent of the total bundle tubes in 2nd-pass mode.